FIG. 1 shows a system in which one Radio Access Network RAN is connected to a plurality of Core Networks CN. Such a RAN is planned to be implemented in the Universal Mobile Telephony System UMTS currently being standardized by ETSI (European Telecommunication Standards Institute), for example. The RAN provides the radio connection for the subscribers of a plurality of core networks and is therefore also called Generic RAN, i.e. GRAN. The services are provided by the core networks connected to the RAN using the Iu interface. In the figure, the GSM, UMTS, GPRS (General Packet Radio Service), and ISDN (Integrated Services Digital Network) core networks are shown. The Mobile Station MS can make connections to the core networks using radio connections to the RAN. The MS makes radio connections to the base stations of the radio access network. The RAN routes the connections to the core network whose service the subscriber is currently using.
Information concerning the location of the mobile station is needed in the radio access network for routing incoming calls and other services provided by the core networks. For location management, the geographical area served by a radio access network is divided into one or a plurality of Location Areas LA. The location of a mobile station is tracked with an accuracy of one location area. Within the location area, the mobile station can move without informing the RAN about its movements. The location area consists of one or a plurality of cells, a cell being the coverage area of a base station. The base stations send information about themselves continuously. This information comprises the identity and the location area of the base station. Based on this information, the mobile station knows the location area it is visiting at all times. Additionally, the mobile knows the identity of the location area of its latest location update, i.e. its currently specified location area. When recognizing that the location area identification sent by the base station having the best signal is different from the location area of the mobile, the mobile initiates a location update procedure. In the procedure, the mobile contacts the RAN to inform it of the new location area.
The size of the location areas is always selected as a compromise. When using very small location areas, the moving mobile stations have to contact the network rather frequently to inform the network about their new location areas. The frequent location updates reserve a lot of radio transmission capacity, which can then not be used for transmission of user information. On the other hand, when using very large location areas, the mobile that is receiving a call has to be paged from a large area comprising lots of base stations thus reserving unnecessary amounts of transmission capacity. Therefore, the optimum size for a location area is a compromise depending on both the mobility of the subscribers and the amount of calls coming to the subscribers.
The location can be defined using different levels of accuracy. When using a packet switched service such as GPRS in the standby state, the location is tracked with an accuracy of a smaller location area, i.e. a routing area. This size of a routing area is smaller than the size of a location area, typically one or a few cells. When there are packets to be transferred, the service moves to the active state. For this, the mobile using the service is paged from the routing area. In the active state the location of the mobile is tracked with an accuracy of one cell. When there are no packets to be sent, the service returns to the standby state after a short delay. When the packet stream continues, the mobile is paged again from the routing area. The mobile has to be paged a plurality of times during one connection. Therefore, the number of pages made during a packet switched connection is generally much larger than the number of paging messages sent by the RAN when the mobile is in the idle state of a circuit switched connection. This is the reason for using smaller locations areas, i.e. routing areas, in packet switched services.
The location information is needed in the RAN in order to provide the radio connections for the services provided by the core networks. Hence, in a system shown in FIG. 1, it is preferable to store the location information in the RAN. The services offered by a core network may also depend on the location of the subscriber, i.e. the subscriber is offered different services in different service areas. Therefore, the location updates of the mobile subscriber have to be passed to the core network as well. This requires signaling and causes an unnecessary load on the Iu interface.
The problem with the prior art is the handling of location information between the RAN and the core networks. The objective of the present invention is to solve this problem. This objective is achieved using the method defined in the independent claim.